CHANGES IN THE RELATIVE CONTRIBUTION OF FREE-LIVING AND ATTACHED BACTERIA TO TOTAL COMMUNITY METABOLISM AND SINGLE-CELL ACTIVITY ALONG A NUTRIENT GRADIENT

Recent studies suggest that the importance of the bacterioplankton community declines as one moves from oligotrophic to eutrophic systems. With this in mind, we used the agriculturally impacted tidal creeks of a small estuarine system to explore changes in respiration and single-cell activity of free-living and attached bacterial communities among systems of different nutrient status. We observed several consistent patterns throughout the sampling season. First, the contribution of free-living bacteria to total water column respiration decreases with increasing nutrient enrichment. Second, this decrease is accompanied by an increase in the contribution of attached bacteria to water column respiration. Third, there is an increase in the proportion of highly-active cells along this gradient and a disproportionate increase among the attached bacterial community. These results suggest that decreases in the contribution of free-living bacteria to total community respiration along a eutrophic gradient may be attributed to the gradual transfer of respiration from free-living bacteria to attached, and eventually benthic, microbial processes.